1. Field of the Invention
The present invention relates to a method and apparatus for improving the electrical performance of a battery. More particularly, it relates to a method and apparatus for improving the discharge efficiency of a portable device battery.
2. Description of the Related Art
Batteries, or battery packs, are used to supply power to those devices such as PDA, notebook, and digital camera by converting chemical energy into electrical power, making thereby the portability possible. Though batteries for portable devices are compact and easy to use, they can only supply power for a limited period of time because their capacities are limited. Typically, a Li-ion or Li-polymer battery can supply power to a notebook only for several hours in normal operating condition. A battery with such a short operating duration restricts the portability of its device and is in conflict with the increasing need for better battery performance and longer operating duration. This is the background wherein the inventor of the present invention conceives the idea of improving the electrical performance of battery to be disclosed below.
A battery is an energy converting apparatus designed to transform chemical energy into electrical energy when discharging and to transform electrical energy back to chemical energy when recharged. Because chemical reactions are involved in the charge and discharge processes of the battery, its electrical characteristics will certainly be under the influence of the temperature of the surrounding environment and the temperature of the battery itself.
FIG. 1 illustrates the discharge temperature characteristics of a typical Li-polymer battery, and FIG. 2 illustrates the discharge temperature characteristics of a typical Li-ion battery according to the prior art. Therein, one may discern that temperature has a positive effect on the discharging battery. That is, as temperature rises, the discharge voltage and the capacity (and capacity ratio) both rise. The phenomenon can be explained by the positive effect of temperature variations on the reaction constants of the chemical reactions involved in the discharge process as understood by one skilled in the art. One may also discern that as temperature rises, the slopes of the voltage-capacity curves decrease, suggesting that the discharge voltage variations decrease as temperature rises. By investigating FIG. 1 and FIG. 2, we conclude that a high operating temperature of a battery stabilizes its discharge voltage and increases its capacity, allowing the battery to supply power for a longer duration.